Cyanide-free liquid composition for immersion gold plating

ABSTRACT

A gold deposition accelerator for electroless gold plating comprising one or more alkali metal compound(s), wherein said alkali metal compound is not a compound comprising only sodium as an alkali metal, and said alkali metal compound is not only halide, only potassium sulfite, or only potassium sodium tartrate of an alkali metal, an electroless gold plating solution comprising said gold deposition accelerator, a gold plating method and a gold deposition accelerating method using the same and the like are provided.

This application is a U.S. National Phase application under 35 U.S.C. § 371 of PCT/JP2016/089007, filed Dec. 27, 2016. The entire disclosure content of this application is herewith incorporated by reference in its entirety into the present application.

TECHNICAL FIELD

The present invention relates to a gold deposition accelerator for use in formation of a gold plating film on an electronic industrial component such as a printed wiring board, an electroless gold plating solution comprising said gold deposition accelerator, and a plating method and a gold deposition accelerating method using said electroless gold plating solution.

BACKGROUND ART

A printed board has a metal circuit pattern on and/or within the board. For the circuit, a metal with a low electrical resistance such as copper is used, and further, a barrier metal layer is provided for preventing an oxidation, corrosion of the circuit and/or preventing a migration with gold. As a metal used as the barrier metal layer, palladium, platinum, silver, cobalt, and an alloy thereof can be used, as well as nickel or a nickel alloy. There is also a technique of forming a palladium layer on a nickel layer in order to prevent a diffusion of nickel due to a thermal treatment. After these substrate metal layers are formed, they are further covered with a gold film to be a complete circuit. However, a gold film is, in general, used for preventing corrosion of a circuit and/or is used as a contact, thus a film with a high porosity is not preferable and a surface with few gaps is required.

As a gold plating method, electrolytic gold plating, autocatalytic electroless gold plating, substrate-catalytic (surface-catalytic) gold plating, and immersion gold plating and the like are known. Autocatalytic electrolytic gold plating performs gold deposition by a reducing agent of which gold is a catalyst. Substrate-catalytic (surface-catalytic) gold plating performs gold deposition by a reducing agent of which a substrate metal is a catalyst. Immersion gold plating performs gold deposition by an electrical displacement reaction between a substrate metal on a surface to be plated and a gold ion and/or a gold ion complex. These plating methods may also be used in combination of two or more kinds.

Although, as for an electroless gold plating solution, many plating solutions containing a cyanide compound as a source of gold have been reported, there are storage and management issues, safety issues during various treatments, as well as a cost issue for a waste liquid treatment. Because of this, a development of an electroless gold plating solution containing no cyanide compound has been desired. Patent Literature 1 describes an electroless plating solution containing two types of reducing agents using water-soluble gold salts such as gold sodium sulfite in place of cyanide compounds, and considers using ethylenediamine tetraacetic acid (EDTA), and oxocarboxylic acids such as tartaric acid and the like, which are generally used as complexing agents, as reaction accelerators. Patent Literature 2 similarly describes an electroless plating solution that uses gold sodium sulfite as a source of gold, and considers using potassium sulfite to improve the gold deposition speed, while the concentration of potassium sulfite is described to be limited to equal to or less than 500 mg/L, since the plating solution becomes unstable and causes self-decomposition when the concentration of potassium sulfite is too large. In Patent Literature 3, a compound which releases a halogen ion having a strong action of promoting an anode reaction is considered as a gold deposition accelerator of an electroless gold plating solution. Patent Literature 4 uses a heavy metal such as thallium salt as a gold deposition accelerator.

PRIOR ART LITERATURES Patent Literatures

-   [PATENT LITERATURE 1] JP, A, 2003-221674 -   [PATENT LITERATURE 2] JP, B, 4758470 -   [PATENT LITERATURE 3] JP, A, 2010-209415 -   [PATENT LITERATURE 4] JP, A, 2007-308796

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

The conventional methods using complexing agents such as oxocarboxylic acids and potassium sulfite as reaction accelerators were to anticipate in the accelerating effect in gold deposition by interfacial complexation in which a complex ion coordinates to a metal ion. However, it was difficult to obtain the desired gold deposition speed only by a complexing agent. This was because a complexing agent, depending on its amount to be added, has a problem of erosion to a substrate, and due to decomposition of the complexing agent itself, makes a plating solution unstable and induces the self-decomposition of the plating solution, thus the amount of the complexing agent to be added needs to be controlled. Also, when reducing agents and stabilizers are included, one must consider the interaction with such ingredients. On the other hand, a gold deposition accelerator using heavy metals such as thallium has an issue with an impact on the environment.

Thus, the present invention is to provide a gold deposition accelerator which readily improves the gold deposition speed of an electroless gold plating solution and enables to form a uniform gold film, an electroless gold plating solution containing said gold deposition accelerator, a gold plating method and a gold deposition accelerating method etc., using the same.

Means to Solve the Problem

While considering a method to accelerate gold deposition without depending on complexing agents, the present inventors found that alkali metal ions influence a gold deposition speed, and as a result of further proceeding of the research, the present invention has been accomplished.

That is, the present invention relates to the following:

[1] A gold deposition accelerator for electroless gold plating comprising one or more alkali metal compound(s), wherein said alkali metal compound is not a compound comprising only sodium as an alkali metal, and said alkali metal compound is not only halide, only potassium sulfite, or only potassium sodium tartrate of an alkali metal. [2] An electroless gold plating solution comprising the gold deposition accelerator according to [1], a water-soluble source of gold and a complexing agent. [3] The electroless gold plating solution according to [2], wherein the concentration of the alkali metal compound is 0.001 to 5 M on an alkali metal ion basis other than sodium. [4] A gold deposition accelerator comprising a rubidium compound and/or cesium compound. [5] An electroless gold plating solution comprising the gold deposition accelerator according to [4], a water-soluble source of gold and a complexing agent. [6] The electroless gold plating solution according to [2], [3] or [5] further comprising a sodium compound. [7] The electroless gold plating solution according to [2], [3], [5] or [6] comprising no cyanide compound. [8] The electroless gold plating solution according to [2], [3], [5], [6] or [7] comprising an acid or a base as a pH regulator. [9] A method of forming a gold plating film comprising a step of applying the electroless gold plating solution according to [2], [3], [5], [6], [7] or [8] on a surface of an electronic industrial component. [10] A method of accelerating gold deposition in electroless gold plating comprising adding one or more alkali metal compound(s) in an electroless gold plating solution, wherein said alkali metal compound is not a compound comprising only sodium as an alkali metal, and said alkali metal compound is not only halide, only potassium sulfite, or only potassium sodium tartrate of an alkali metal. [11] The method according to [10], wherein the concentration of the alkali metal compound is 0.001 to 5 M on an alkali metal ion basis other than sodium. [12] A method of accelerating gold deposition in electroless gold plating by adding a rubidium compound and/or cesium compound. [13] The method according to [12], wherein the concentration of the rubidium compound and/or cesium compound is 0.001 M to 5 M on a rubidium ion and/or cesium ion basis.

Effects by the Invention

According to the present invention, it can readily improve the gold deposition speed of an electroless gold plating solution, thus, it can realize a sufficient gold deposition speed even in an electroless gold plating solution which does not have a cyanide compound as a source of gold and has a slow deposition speed. Also, since the gold deposition speed can be regulated only by regulating the concentration of alkali metal ions other than sodium, a regulation by many ingredients is possible as compared to when gold deposition is accelerated depending only on a complexing agent, thus being able to provide a more stable electroless gold plating solution. Furthermore, since the deposition speed can be improved without increasing the concentration of gold, an inexpensive plating solution can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a FIGURE comparing gold deposition speeds when alkali metal ions are changed.

EMBODIMENTS FOR CARRYING OUT INVENTION

The gold deposition accelerator of the present invention comprises an alkali metal compound.

The gold deposition accelerating action of the gold deposition accelerator of the present invention is of an alkali metal ion, and the alkali metal compound comprised in the gold deposition accelerator of the present invention may be anything that dissociates to generate an alkali metal ion. Surprisingly, although it is the same alkali metal ion, a sodium ion does not accelerate the gold deposition reaction. Thus, the alkali metal compound comprised in the gold deposition accelerator of the present invention is not a compound comprising only sodium as an alkali metal, but may comprise sodium as long as an alkali metal other than sodium is present. Such compounds include, for example, potassium sodium tartrate.

The alkali metal compound comprised in the gold deposition accelerator of the present invention is preferably one or more selected from the group consisting of a potassium compound, rubidium compound and cesium compound, and more preferably, in terms of deposition accelerativity, a rubidium compound and/or cesium compound. In terms of cost, a potassium compound is also preferable.

The alkali metal compound comprised in the gold deposition accelerator of the present invention includes, but not limited to the following compounds. For example, carbonates such as potassium carbonate, rubidium carbonate, cesium carbonate; nitrates such as cesium nitrate, rubidium nitrate, cesium nitrate; sulfates such as potassium sulfate, rubidium sulfate, cesium sulfate; halides are included, and as halides, fluorides such as potassium fluoride, rubidium fluoride, cesium fluoride; chlorides such as potassium chloride, rubidium chloride, cesium chloride; bromides such as potassium bromide, rubidium bromide, cesium bromide; iodides such as potassium iodide, rubidium iodide, cesium iodide are included. These compounds may be used alone or in combination of two or more.

A counterion to an alkali metal ion in said compound is not particularly limited. As said counterion, carbonate ion, nitrate ion, sulfate ion, sulfite ion, phosphate ion, borate ion, halide ion; carbonate ion such as formate ion, acetate ion, propionate ion, butanoate ion, pentanoate ion, hexanoate ion, heptanoate ion, octanoate ion; hydroxy acid ions such as glycolate ion, lactate ion, malate ion, citrate ion, tartrate ion, isocitrate ion, salicylate ion; aromatic carboxylate ions such as benzoate ion, phthalate ion; dicarboxylate ions such as oxalate ion, malonate ion, succinate ion, glutarate ion, adipate ion, fumarate ion, maleate ion are included, for example. These compounds may be used alone or in combination of two or more.

Alkali metal compounds other than compounds having the above-mentioned counterion include, but not limited to, the following compounds. For example, oxide, peroxide, hydroxide, chromic acid compound, tungstic acid compound, selenic acid compound, molybdic acid compound, orthomolybdic acid compound, niobic acid compound, permanganic acid compound, azide compound, amide compound, toluene sulfonic acid compound, hydride, picric acid compound, tetrahydroboric acid compound, hexafluorosilicic acid compound, perrhenic acid compound, periodic acid compound, iodic acid compound, nitrous acid compound, phosphinic acid compound, nitrobenzene sulfonic acid compound, benzenesulfonic acid compound, alkoxide compound, hydrogen carbonate compound, methacrylic acid compound etc. of alkali metals are included. These compounds may be used alone or in combination of two or more.

As such, the gold deposition accelerator of the present invention may be an alkali metal compound itself, or may be a composition comprising said compound. The composition may be a mixture consisting of two or more alkali metal compounds. Also, the composition may comprise water, a solvent such as organic solvent, in addition to one or more alkali metal(s).

In the gold deposition accelerator of the present invention, the alkali metal compound comprised in the gold deposition accelerator is not only halide, only potassium sulfite, or only potassium sodium tartrate of an alkali metal.

In one embodiment of the gold deposition accelerator of the present invention, the alkali metal compound comprised in the gold deposition accelerator is not only sulfite.

In one embodiment of the gold deposition accelerator of the present invention, the alkali metal compound comprised in the gold deposition accelerator is not only tartrate.

In one embodiment of the gold deposition accelerator of the present invention, when the gold deposition accelerator comprises only a potassium compound as an alkali metal compound, it comprises a potassium compound other than potassium compounds selected from potassium halide, potassium sulfite, and potassium sodium tartrate.

The gold deposition accelerator of the present invention, in the plating solution comprising said gold deposition accelerator, can use an alkali metal compound comprising an alkali metal other than sodium by regulating the concentration on an alkali metal ion basis other than sodium to equal to or more than 0.001 M, preferably equal to or more than 0.01 M, more preferably equal to or more than 0.02 M. In terms of deposition accelerativity, said concentration may be regulated to 0.001 M to 5 M, more preferably 0.01 M to 2 M, particularly preferably 0.02 M to 0.5 M. Since a concentration dependency is also recognized for the gold deposition speed, the desired gold deposition speed can be regulated by regulating the concentration.

In one embodiment of the present invention, the gold deposition accelerator of the present invention does not comprise potassium sodium tartrate.

In one embodiment of the present invention, when the gold deposition accelerator of the present invention comprises potassium sodium tartrate or tartrate, it is preferable to use potassium sodium tartrate in the plating solution by regulating the concentration thereof to equal to or more than 0.11 M, preferably more than 0.11 M, more preferably equal to or more than 0.2 M. In terms of deposition accelerativity, said concentration is preferably 0.11 M to 5 M, more preferably 0.11 M to 2 M, particularly preferably 0.11 M to 0.5 M.

In one embodiment of the present invention, the gold deposition accelerator of the present invention does not comprise potassium sulfite.

In one embodiment of the present invention, when the gold deposition accelerator of the present invention comprises potassium sulfite or sulfite, it is preferable to use potassium sulfite in the plating solution by regulating the concentration thereof to equal to or more than 0.004 M. In terms of deposition accelerativity, said concentration is preferably 0.004 M to 5 M, more preferably 0.01 M to 2 M, particularly preferably 0.02 M to 0.5 M.

The present invention also relates to an electroless gold plating solution comprising the above-mentioned gold deposition accelerator of the present invention, a water-soluble source of gold and a complexing agent.

In the electroless gold plating solution comprising the gold deposition accelerator of the present invention, the concentration of the alkali metal compound is preferably equal to or more than 0.001 M, more preferably equal to or more than 0.01 M, particularly preferably equal to or more than 0.02 M on an alkali metal ion basis other than sodium. In terms of deposition accelerativity, said concentration is preferably 0.001 M to 5 M, more preferably 0.01 M to 2 M, particularly preferably 0.02 M to 0.5 M. Since a concentration dependency to a certain extent is also recognized for the gold deposition speed, the desired gold deposition speed can be regulated by regulating the concentration.

As a source of gold used for the present invention, water-soluble gold salts such as a gold sulfite salt and a chloroauric acid salt can be used, in particular. It is preferable to use a source of gold comprising no cyanide in terms of safety and waste water treatment issues. The concentration of the source of gold is preferably 0.1 to 10 g/L, even preferably 0.5 to 5 g/L. When sodium gold sulfite is used for example, its concentration range is preferably 0.1 to 10 g/L, even preferably 0.5 to 5 g/L on a gold concentration basis, considering the property of the deposition film. In one embodiment of the present invention, the source of gold does not comprise any alkali metal other than sodium. Also, in one embodiment of the present invention, the gold deposition accelerator of the present invention comprises an alkali metal compound comprising no gold.

In one embodiment of the present invention, when the source of gold comprises an alkali metal other than sodium, the electroless gold plating solution of the present invention further comprises an alkali metal compound comprising no gold, and in this case, the concentration of the alkali metal ion other than sodium in the electroless gold plating solution is preferably equal to or more than 0.001 M, more preferably equal to or more than 0.01 M, particularly preferably equal to or more than 0.02 M. In terms of deposition accelerativity, said concentration is preferably 0.001 M to 5 M, more preferably 0.01 M to 2 M, particularly preferably 0.02 M to 0.5 M. The concentration of said alkali metal ion is the combined concentration of the alkali metal ion derived from the source of gold and the alkali metal ion derived from the above-mentioned alkali metal compound comprising no gold (not including sodium ion).

The complexing agent used for the present invention is not particularly limited, but include, for example in particular, a compound capable of forming a complex with a monovalent or trivalent gold ion such as sulfite, thiosulfite, and the like. The concentration of the complexing agent is preferably 0.001 M to 5 M, even preferably 0.01 M to 0.5 M, and when sodium sulfite is for example used as a complexing agent, its concentration range is preferably 0.001 to 5 M, even preferably 0.01 to 0.5 M.

As a pH regulator, various acids such as sulfuric acid, hydrochloric acid, phosphoric acid; hydroxide salts such as potassium hydroxide; and amines such as NR₄OH (R: hydrogen or alkyl) with a restriction and the like can be used for example. When a phosphate buffer is used for example as a pH regulator, it is preferable to perform by phosphoric acid and sodium hydroxide or potassium hydroxide.

pH is preferably in the range of 5 to 11, even preferably 6 to 10, depending on its composition.

While the gold deposition accelerator of the present invention can be added to a plating solution for electroless gold plating, said plating solution can also be used for any of the methods of autocatalytic electroless gold plating, substrate-catalytic (surface-catalytic) gold plating, immersion gold plating and plating in combination thereof. Particularly, in terms of deposition accelerativity, it is preferable to be used for immersion gold plating.

The plating solution of the present invention may or may not comprise a reducing agent. The reducing agent includes ascorbates such as sodium ascorbate; hydroxylamine or salts of hydroxylamine such as hydroxylamine hydrochloride, hydroxylamine sulfate; hydroxylamine derivatives such as hydroxylamine-O-sulfonic acid; hydrazine; amine borane compounds such as dimethylamine borane; boron hydride compounds such as sodium boron hydride, sugars such as glucose; hypophosphites, etc. These reducing agents may be used alone or in combination of two or more. Furthermore, any compound judged to be capable of depositing gold by reduction from gold ions or gold complexes according to the Nernst equation may be used, but is used in consideration of the reactivity toward other bath components, the bath stability, etc.

The plating solution of the present invention can use other additives such as grain-shape regulator, brightener in an appropriate range of concentration. Other additives are not particularly limited, and additives that have conventionally been used can be used for example. Namely, grain-shape regulators such as polyethylene glycol, brighteners such as thallium, copper, antimony, lead are included. Any other additives besides these additives can be used as long as they meet the above-mentioned condition.

In one embodiment of the present invention, the electroless gold plating solution of the present invention does not comprise potassium sodium tartrate.

In one embodiment of the present invention, when the electroless gold plating solution of the present invention comprises potassium sodium tartrate or tartrate, it is preferable to use potassium sodium tartrate in the plating solution by regulating the concentration thereof to equal to or more than 0.11 M, preferably more than 0.11 M, more preferably equal to or more than 0.2 M on an alkali metal ion basis other than sodium. In terms of deposition accelerativity, said concentration is preferably 0.01 M to 5 M, more preferably 0.01 M to 2 M, particularly preferably 0.01 M to 0.5 M.

In one embodiment of the present invention, the electroless gold plating solution of the present invention does not comprise potassium sulfite.

In one embodiment of the present invention, when the electroless gold plating solution of the present invention comprises potassium sulfite, it is preferable to use potassium sulfite in the plating solution by regulating the concentration thereof to equal to or more than 0.004 M. In terms of deposition accelerativity, said concentration is 0.004 M to 5 M, more preferably 0.01 M to 2 M, particularly preferably 0.02 M to 0.5 M.

In one embodiment of the electroless gold plating solution of the present invention, when the electroless gold plating solution comprises only a potassium compound as an alkali metal compound, it comprises a potassium compound other than potassium compounds selected from potassium halide, potassium sulfite and potassium sodium tartrate.

The present invention also relates to a gold deposition accelerator comprising a rubidium compound and/or cesium compound. Gold deposition is accelerated by a rubidium ion and cesium ion. The concentration of the rubidium ion is preferably 0.001 to 5 M, more preferably 0.01 to 2M, particularly preferably 0.02 to 0.5 M. The concentration of the cesium ion is preferably 0.001 to 5 M, more preferably 0.01 to 2 M, particularly preferably 0.02 to 0.5 M. Examples of rubidium compounds and/or cesium compounds include the similar compounds included as the examples for the above-mentioned alkali metal compounds.

The gold deposition speed of the electroless gold plating solution comprising the gold deposition accelerator of the present invention may be equal to or more than 0.003 μm/min, preferably equal to or more than 0.004 μm/min, more preferably equal to or more than 0.005 μm/min on 4 cm² Ni substrate at pH 7, bath temperature of 80° C.

The present invention also relates to a method of forming a gold plating film comprising a step of applying the electroless gold plating solution of the present invention on a surface of an electronic industrial component. In terms of deposition speed, the operating temperature of the electroless gold plating solution in said step is preferably 20 to 90° C., more preferably 40 to 70° C. In terms of the liquid stability and deposition speed, pH is preferably 5 to 11, more preferably 6 to 10. The electronic industrial component is not particularly limited, but typically includes electrodes, wirings, etc.

The present invention also relates to a method of accelerating gold deposition in electroless gold plating comprising adding one or more alkali metal compound(s) in an electroless gold plating solution, wherein said alkali metal compound is not a compound comprising only sodium as an alkali metal, and said alkali metal compound is not only halide, only potassium sulfite, or only potassium sodium tartrate of an alkali metal.

The concentration of said alkali metal compound in the method of accelerating gold deposition of the present invention may be 0.001 to 5 M, preferably 0.01 to 2 M, more preferably 0.02 to 0.5 M on an alkali metal ion basis other than sodium.

In one embodiment of the present invention, the method of accelerating gold deposition of the present invention does not comprise potassium sodium tartrate.

In one embodiment of the present invention, when the method of accelerating gold deposition of the present invention comprises potassium sodium tartrate, it is preferable to use potassium sodium tartrate in the plating solution by regulating the concentration thereof to equal to or more than 0.11 M, preferably more than 0.11 M, more preferably equal to or more than 0.2 M on a potassium ion basis. In terms of deposition accelerativity, said concentration is preferably 0.11 M to 5 M, more preferably 0.11 M to 2 M, particularly preferably 0.11 M to 0.5 M.

In one embodiment of the present invention, the method of accelerating gold deposition of the present invention does not comprise potassium sulfite.

In one embodiment of the present invention, when the method of accelerating gold deposition of the present invention comprises potassium sulfite, it is preferable to use potassium sulfite in the plating solution by regulating the concentration thereof to equal to or more than 0.004 M. In terms of deposition accelerativity, said concentration is preferably 0.004 M to 5 M, more preferably 0.01 M to 2 M, particularly preferably 0.02 M to 0.5 M.

The present invention also relates to a method of accelerating gold deposition in electroless gold plating by adding a rubidium compound and/or cesium compound. Preferably, the total concentration of the rubidium compound and/or cesium compound is preferably 0.001 M to 5 M, more preferably 0.01 M to 1 M on a rubidium ion and/or cesium ion basis. When only a rubidium compound is added, its preferable concentration is 0.001 M to 5 M, more preferably 0.01 M to 1 M on a rubidium ion basis. When only a cesium compound is added, a preferable concentration is 0.001 M to 5 M, more preferably 0.001 M to 1 M on a cesium ion basis.

The present invention also relates to, in another embodiment, a method of accelerating gold deposition in electroless gold plating, wherein the concentration of an alkali metal ion in an electroless gold plating solution is regulated to regulate a gold deposition speed.

The concentration of the total alkali metal ions in the electroless gold plating solution is regulated to be 0.001 M to 5 M, preferably 0.01 M to 2 M, more preferably 0.02 M to 0.5 M.

WORKING EXAMPLES

The electroless gold plating solution of the present invention is explained further in detail below by reference to working examples and comparative examples, which however are not to limit the present invention in any way. A copper plate was used as a plating sample, and this was subjected to Ni alloy plating by the procedure below and used for testing.

Comparative Examples 1-3

The sources of gold, the complexing agents in Table 1 were mixed in the concentrations in Table 1 to prepare gold plating solutions, and pH of the gold plating solutions were regulated to pH 7.0 by using phosphoric acid as a pH regulator. A 4 cm² Ni rolling plate was used, plating was performed for 10 minutes at 80° C., the film thickness was measured, and the deposition speed was calculated.

Working Examples 1-6

The sources of gold, the complexing agents, the deposition accelerators in Table 1 were mixed in the concentrations in Table 1 to prepare gold plating solutions, and pH of the gold plating solutions were regulated to pH 7.0 by using phosphoric acid as a pH regulator. A 4 cm² Ni rolling plate was used, plating was performed for 10 minutes at 80° C., the film thickness was measured, and the deposition speed was calculated. For the gold plating film thickness, “FT-9500X”, X-ray fluorescence film thickness meter by Hitachi was used.

TABLE 1 Composition of plating solutions and plating conditions Comparative Working Working Working Working example 1 example 1 example 2 example 3 example 4 Substrate Ni Ni Ni Ni Ni Source of Sodium gold mol/L  0.005  0.005  0.005  0.005  0.005 gold sulfite as Au Sodium mol/L — — — — — chloroaurate as Au Complexing Sodium mol/L 0.1 0.1  0.1  0.1  0.1 agent sulfite Sodium mol/L — — — — — thiosulfate Potassium mol/L — 0.05 — — — carbonate Deposition Rubidium mol/L — — 0.05 — — accelerator carbonate Cesium mol/L — — — 0.05 — carbonate Cesium mol/L — — — — 0.1 chloride pH regulator Phosphoric Phosphoric Phosphoric Phosphoric Phosphoric acid acid acid acid acid pH 7.0 7.0  7.0  7.0  7.0 Bath 80° C. 80° C. 80° C. 80° C. 80° C. temperature Deposition  0.03 0.05 0.06 0.08  0.05 speed(μm/ 10 min) Comparative Working Comparative Working example 2 example 5 example 3 example 6 Substrate Ni Ni Ni Ni Source of Sodium gold mol/L 0.005 0.005  0.005  0.005 gold sulfite as Au Sodium mol/L 0.005 0.005 — — chloroaurate as Au Complexing Sodium mol/L 0.1  0.1  — — agent sulfite Sodium mol/L — — 0.05 0.05 thiosulfate Potassium mol/L — — — — carbonate Deposition Rubidium mol/L — — — — accelerator carbonate Cesium mol/L — 0.05  —  0.005 carbonate Cesium mol/L — — — — chloride pH regulator Phosphoric Phosphoric Phosphoric Phosphoric acid acid acid acid pH 7.0  7.0  7.0  7.0  Bath 80° C. 80° C. 80° C. 80° C. temperature Deposition 0.02  0.05  0.24 0.41 speed(μm/ 10 min)

FIG. 1 is of a comparison of deposition speeds when an alkali metal ion is changed based on the results of comparative example 1, working examples 1-3 of Table 1. It was recognized that a gold deposition speed improves by adding an alkali metal ion. In addition, it was recognized that a gold deposition speed depends on an alkali metal ion, since working example 1, working example 2 and working example 3 have different gold deposition speeds in spite of them all comprising a carbonate ion in the same concentration.

It was recognized that, for an electroless gold plating solution containing a gold deposition accelerator comprising at least one or more alkali metal ion(s) other than a sodium ion, the gold deposition speed is large as compared to an electroless gold plating solution comprising no gold deposition accelerator, even after changing the kinds of cesium salt, source of gold and complexing agent.

INDUSTRIAL APPLICABILITY

By the present invention, a sufficient gold deposition speed can be realized even in electroless plating using an electroless gold plating solution which does not have cyanide compound as a source of gold and has a slow deposition speed. 

1. A gold deposition accelerator for electroless gold plating comprising one or more alkali metal compound(s), wherein said alkali metal compound is not a compound comprising only sodium as an alkali metal, and said alkali metal compound is not only halide, only potassium sulfite, or only potassium sodium tartrate of an alkali metal.
 2. An electroless gold plating solution comprising the gold deposition accelerator of claim 1, a water-soluble source of gold and a complexing agent.
 3. The electroless gold plating solution of claim 2, wherein the concentration of the alkali metal compound is 0.001 to 5 M on an alkali metal ion basis other than sodium.
 4. A gold deposition accelerator comprising a rubidium compound and/or cesium compound.
 5. An electroless gold plating solution comprising the gold deposition accelerator of claim 4, a water-soluble source of gold and a complexing agent.
 6. The electroless gold plating solution of claim 5, further comprising a sodium compound.
 7. The electroless gold plating solution of claim 5, comprising no cyanide compound.
 8. The electroless gold plating solution of claim 5, comprising an acid or a base as a pH regulator.
 9. A method of forming a gold plating film comprising a step of applying the electroless gold plating solution of claim 5 on a surface of an electronic industrial component.
 10. A method of accelerating gold deposition in electroless gold plating comprising adding one or more alkali metal compound(s) in an electroless gold plating solution, wherein said alkali metal compound is not a compound comprising only sodium as an alkali metal, and said alkali metal compound is not only halide, only potassium sulfite, or only potassium sodium tartrate of an alkali metal.
 11. The method of claim 10, wherein the concentration of the alkali metal compound is 0.001 M to 5 M on an alkali metal ion basis other than sodium.
 12. A method of accelerating gold deposition in electroless gold plating by adding a rubidium compound and/or cesium compound.
 13. The method of claim 12, wherein the concentration of the rubidium compound and/or cesium compound is 0.001 M to 5 M on a rubidium ion and/or cesium ion basis.
 14. The electroless gold plating solution of claim 2, further comprising a sodium compound.
 15. The electroless gold plating solution of claim 2, comprising no cyanide compound.
 16. The electroless gold plating solution of claim 2, comprising an acid or a base as a pH regulator.
 17. A method of forming a gold plating film comprising a step of applying the electroless gold plating solution of claim 2 on a surface of an electronic industrial component. 